QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-H ACTIVE RESET ISOLATED 9-36V INPUT TO 48V @1.5A DC/DC POWER CONVERTER LT1952-1 DESCRIPTION Demonstration circuit 1317A-H is isolated input to 48V output 1/8th Brick footprint converter featuring the LT®1952 switching controller with Active Reset circuit. The Active Reset circuit can improve the efficiency in wide input voltage applications. Also, the Active Reset allows the implementation of self-driven synchronous secondary rectifiers in some applications. The DC1317A-H (Figure 7) converts isolated 9V to 36V input to 48V output and provides over 1.5A of output current depending on cooling. When determining the cooling requirements the actual input voltage range and continuous maximum output current must be taken into account. The converter operates at 150kHz with the peak efficiency greater than 90%. The DC1317 can be easily modified to generate output voltages in the range from 0.6V to 48V. The output currents of DC1317A demo board are limited by total output power of up to 150W. Demo boards DC830A and DC677A are recommended for higher output power levels of up to 500W. The available versions of DC1317A are: DC1317A-E, 36-72Vin to 5V, 12A DC1317A-F, 9-36Vin to 3.3V, 22A * DC1317A-F5, 9-36Vin to 5V, 20A DC1317A-G, 9-36Vin to 12V, 8A * DC1317A-G18, 9-36Vin to 18V, 5A DC1317A-H, 9-36Vin to 48V, 1.5A * The *DC1317A-G18 is a slightly modified design featuring 18V @6A output. Please contact the LTC factory for details. The DC1317 circuit features soft-start which prevents output voltage overshoot on startup or when recovering from overload condition. The DC1317 has precise over-current protection circuit that allows for continuous operation under short circuit conditions. The low power dissipation under short circuit conditions insures high reliability even during short circuits. The LT1952 can be synchronized to an external clock of up to 400kHz. Please refer to LT1952 data sheet for design details and applications information. DC1317A-A, 34-75Vin to 3.3V, 35A DC1317A-B, 18-72Vin to 5V, 25A Design files for this circuit board are avail available. Call the LTC factory. DC1317A-C, 18-72Vin to 12V, 8A-12A DC1317A-D, 18-72Vin to 24V, 5A LT is a trademark of Linear Technology Corporation Table 1. Performance Summary PARAMETER CONDITION VALUE Minimum Input Voltage IOUT = 0A to 1.5A 9V Maximum Input Voltage IOUT = 0A to 5A 36V VOUT VIN = 9V to 36V, IOUT = 0A to 2A 48V ±3% Typical Output Ripple VOUT VIN = 18V to 72V, IOUT = 0A to 5A 100mVP–P Nominal Switching Frequency 150kHz 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-H ACTIVE RESET ISOLATED 9-36V INPUT TO 48V @1.5A DC/DC POWER CONVERTER QUICK START PROCEDURE PROCEDURE Demonstration circuit 1317 is easy to set up to evaluate the performance of LT1952-1 circuit. Refer to Fig Fig ure 1 for proper measurement equipment setup and follow the procedure below: NOTE: When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. See Figure 2. for proper scope probe technique. 1. With power off, connect the input power supply to Vin and GND. Make sure that the input power supply has sufficient current rating at minimum input voltage for the required output load. 2. Turn on the power at the input. NOTE: Make sure that the input voltage does not exceed 36V including transients. 3. Check for the proper output voltage. Vout = 48V. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 4. Once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 5. The DC1317 is equipped with an output capacitor CSYS (100uF) that approximates typical system rail capacitance. If system board already has capacitance of similar value CSYS can be removed. 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-H ACTIVE RESET ISOLATED 9-36V INPUT TO 48V @1.5A DC/DC POWER CONVERTER Figure 1. Proper Measurement Equipment Setup Figure 2. Scope Probe Placement for Measuring Input or Output Rip Rip ple ACTIVE RESET CIRCUIT The Active Reset circuit on DC1317A-H demo board consists of a small P-Channel MOSFET Q13 and reset capacitor C25. The MOSFET Q13 is used to connect the reset capacitor across the transformer T1 primary winding during the reset period when Q1 MOSFET is off. The voltage across capacitor C25 automatically adjusts with the duty cycle to provide complete transformer reset under all operating conditions. Also the active reset circuit shapes the reset voltage into a square waveform that results in lower drain voltages for Q1 and Q2 MOSFETs. The lower MOSFET drain voltages allow lower voltage and lower Rdson MOSFETs to be used. The MOSFETs must be avalanche rated for the peak-reset voltage. If non-avalanche rated MOSFETs are used a proper drain voltage de-rating should be used. The main benefit of active reset circuit in the case of DC1317A-H demo board is high efficiency (shown in Figure 3), wide input range, high power density 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-H ACTIVE RESET ISOLATED 9-36V INPUT TO 48V @1.5A DC/DC POWER CONVERTER and small size. To achieve such high efficiency all of the power components were carefully selected. Please consult LT factory for assistance if any changes to the circuit are required. LT1952 Efficiency 12V in to 48V out 92% Efficiency 90% 88% 86% 24V input 12V input 84% 0.0 0.4 0.8 1.2 1.6 2.0 Iout [A] Figure 3. High efficiency of DC1317ADC1317A-H al allows the board to be used in thermally critical appliapplications. Up to 2A of output current can be drawn with proper air flow. Figure 5. Fast transient response of DC1317ADC1317A-H is superior to many competing power modules without the additional output capaci capacitors. SOFT START FUNCTION The DC1317 features LT4430 opto coupler driver that has soft start function which produces monotonic startup ramp shown if Figure 6. The rise time of output voltage is controlled by capacitor C19. Also, the soft-start function will prevent input current surges even with full load at the output. OUTPUT LOAD STEP RESPONSE RESPONSE The load step response of DC1317A-H is very fast even though relatively small amount of output capacitance is present (6.8uF ceramic and 33uF low ESR electrolytic). This is thanks to fast error amplifier of LT4430, optimal amount of current slope compensation of LT1952, fast opto coupler and fast error amplifier of LT1952. If higher load steps need to be handled more output capacitance can be added in order to keep the voltage transients at the desired level. The load step transients are shown in Figure 5. Figure 6. The LT4430 opto coupler driver proproduces monotonic output voltage rise at startup without out out put voltage overshoot. overshoot. 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-H ACTIVE RESET ISOLATED 9-36V INPUT TO 48V @1.5A DC/DC POWER CONVERTER DEBUGGING AND TESTING TESTIN G The DC1317 can easily be tested and debugged by powering the bias circuit separately from the main power circuit. To place DC1317 into debug mode remove the resistor R1 and connect 12V, 100mA power source to +Vb node (right side of R1). By doing this, the primary PWM controller LT1952 can be activated without the main primary power being applied to +Vin. case of C6. Please modify the reference designators in your schematic to reflect the actual component used. The following simple PCB layout rules should be helpful. If possible use solid ground planes on layers 2 and n-1. The ground planes will prevent the switching noise from coupling into sensitive lines. Place sensitive lines on the inner layers that will be shielded by grounds on layers 2 and n-1. To activate the LT4430 control circuit, feed 5V, 100mA power source into pin 1 of LT4430 controller via a diode. Keep the loop formed by Q1, RCS1, Cin and T1 tight. Once the primary and secondary controllers are running the main power (+Vin) can be applied slowly while observing the switching waveforms and output voltage. Keep noise sensitive nodes like SD/VSEC, ROSC, FB, COMP, ISENSE, BLANK and DELAY as small as possible by placing the associated components close to the LT1952 and LT4430 chips. The input current supplying the power transformer T1 should not exceeded 200mA without the output load. If one of the MOSFETs is damaged, the input current will exceed 200mA. Use local vias for all components that connect to ground planes. PCB LAYOUT The PCB layout should be carefully planned to avoid potential noise problems. The PCB layout for DC1317A can be used as a guide. Since demo board DC1317A has 8 versions the PCB layout has optional components that can be removed. The schematic in figure 7 is showing the circuit without any optional components. Also, the circuit in figure 7 does not show any zero-ohm resistors. Please consult the schematic on page 7 to determine if any of the options should be included in your PCB layout. Keep the loop formed by Q2, Q3 and T1 tight. Do not place any traces on the layers 2 and n-1 to avoid ground planes from being compromised. If the PCB layout has to be done on 2 or 4-layer PCB try to stay close to the guidelines outlined above. Also, maximize the ground connections between components by placing the components tight together. Please contact LT factory for additional assistance. Also, the PCB layout has a common schematic that is used just for the layout. The PCB layout schematic is not included in this quick start guide but it is included with PCB design files. Please note that the actual circuit schematic on page 7 shows the component values. The PCB layout schematic included with design files does not show the component values. In some cases, a different component like a diode is used in a place holder for a capacitor such as in the 5 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-H ACTIVE RESET ISOLATED 9-36V INPUT TO 48V @1.5A DC/DC POWER CONVERTER D2 BAS516 1.5mH +Vin 2.2R R11 10k Cin1 Cin2 Cin3 6.8uF, 50V -Vin 6 D5 PDZ10B +Vout *Q3 PDU540 10, 11 T1 D6 BAS516 G45R2-0324.006 SW0 U2 LTC4440-5 5 R10 Vu1 1 C3 1u 2 3 1 Vfb 2 R15 249k 3 R42 0R 4 5 SS C10 0.1u 6 R22 7 13.3k 8 Comp Sout FB=1.23V Vin Rosc Out Sync PGND MaxDC Delay Vr=2.5V OC SD Isense GND Blank R28 143k R32 143k +Vr2 TG Inp TS RJK0653 C5 2.2u Rcs1 4 D9 PDZ7.5B 0.005R Vu1 *R29 PMEG3002 R2 560k 16 R26 220R Vu1 U4 LT4430 U6 PS2801-1 1 D10 14 Cu1 4.7u BAT760 C16 0.22u Vfb C23 1uF R20 470k 12 11 10 D11 BAS516 Sout 15 13 Q9 BCX55 43k 5 R23 2.4k R9 47R 9 C13 .47u SW0 Vcc R27 470R Opto GND Comp SS FB C19 1uF, X5R 6 5 4 C17 15n R34 19.6k R35 487k +Vo1 R38 6.04k C15 2.2nF, 2kV Demo Board DC1317A-H schematic R53 200R * Please change the ref designator to reflect the symbol. NOTE: BAS516 Sout R30 1.2k R54 2.2R D17 R33 158k 2 3 C11 3.3n R24 22k SS +Vb GND 6 U1 LT1952-1 R14 33K Q12 BC856T Boost Q1 C25 33n, 200V R13 22K Vcc Csys 33u, 63V, HVH + GND 2 +Vin +Vo1 7, 8 *Q2 PDS3200 D3 BAS516 +Vr2 9V-36V Input L1 HR-PQA2050-220-LTC 1 6.8uF, X7R Q10 PBSS8110 Vu1 +Vb R1 Co1 L2 +Vin C33 Q13 Si9407 0.1u R45 10k C34 0.33u, 100V This schematic shows only the components required for operation of -H version of DC1317A demo board. All optional components of DC1317A demo board have been removed. Also, all zero-ohm resistors have been replaced with wires. Please consult the full DC1317A-H schematic to decide if any of the optional components should be included in your design. D14 BAS516 6 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-H ACTIVE RESET ISOLATED 9-36V INPUT TO 48V @1.5A DC/DC POWER CONVERTER 7 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-H ACTIVE RESET ISOLATED 9-36V INPUT TO 48V @1.5A DC/DC POWER CONVERTER 8